1. Field of the Invention
The present invention relates to an electronic watermark embedding apparatus, an electronic watermark embedding method and a record medium having an electronic watermark for embedding an electronic watermark for limiting duplication into contents comprised of digital information and a manufacturing method thereof.
2. Description of the Related Art
As digital TV broadcasting has been realized, distribution of images by digital signals is becoming popular. Also wide spread is a video recorder for recording the image as digital data on an optical disk, a magnetic tape and so on. Such a video recorder allows images recorded as digital data to be duplicated without deterioration. For this reason, it is necessary to limit the duplication of images from the viewpoint of copyright and so on.
For instance, the watermark (electronic watermark) technology disclosed in Japanese Patent Laid-Open No. 2000-173175 is one of the technologies for limiting the duplication of the image, and is the technology for embedding information on limitation of the duplication of a digital image. Hereafter, the information on the limitation of the duplication to be embedded into the digital image is called a “watermark.” The watermark is embedded so as to be hidden in the image. For this reason, the embedding of the watermark hardly degrades the quality of the image. In addition, it is likely that a person having received the image having the watermark embedded therein cannot even recognize that the watermark exists in the image, and so it is extremely difficult to eliminate the watermark from the image.
The Japanese Patent Laid-Open No. 2000-173175 discloses a system using the watermark indicating prohibition of the duplication and the watermark indicating permission of one-generation duplication. As such a system can manage the number of times of the duplication, it will not cause a copyright problem and a viewer of a TV broadcast can see a distributed image without being bound by broadcasting time.
According to this system, when the digital image is inputted to the video recorder, the video recorder determines whether or not the watermark exists in the image. If the watermark exists therein and indicates the prohibition of the duplication, the video recorder does not record the image. If no watermark exists therein or the watermark exists therein and indicates the one-generation duplication permission, the video recorder determines that it is allowed to duplicate the image once, and records the image on the optical disk for instance. At this time, if the watermark indicates the one-generation duplication permission, the video recorder embeds the watermark indicating the prohibition of the duplication into the image and records it.
In the case of producing package media such as a video tape or a DVD or in the case of distributing the image from a broadcast station, a noise reduction process for reducing a noise component of the image may be performed. There are also the cases where a bit rate of compression in performing compression recording is changed according to a work or the bit rate of compression is switched within the work. In the case of embedding the watermark into the image contents, however, the watermark is influenced by intensity of the noise reduction process and the bit rate of compression in recording the image contents. Since a degree of degradation of the watermark changes in conjunction with the intensity of these processes, the degree of degradation increases when the intensity of the noise reduction process is increased or the bit rate of compression is decreased (compression ratio is increased) for instance, so that it may become difficult to read the watermark on reproduction.
In the case where the intensity of the noise reduction process is increased or the bit rate of compression is decreased, the image of that portion normally tends to become flat. However, the watermark is apt to be prominent in a flat image, and so it should be embedded with decreased intensity. For this reason, if there continues to be a state of high intensity of the noise reduction process or a state of low bit rate of compression, there also continues to be the state of low intensity of the watermark consequently, and thus it may become difficult to detect the watermark.